Analysis of Variance (ANOVA) is a statistical test used when comparing the means of multiple groups. It assesses whether there are statistically significant differences between the group means, making option C the correct answer.

The attention mechanism in NLP allows a model to pay different amounts of attention to different words when processing a sequence. This mechanism is a fundamental component of transformer-based models like BERT and GPT, enabling them to capture contextual information and understand word relationships in sentences, paragraphs, or documents.

To retrieve all the records from a table named "Employees" in a relational database like MySQL, you would use the SQL command: SELECT * FROM Employees. The SELECT * statement retrieves all columns and rows from the specified table, effectively fetching all the records.

Ensemble methods in machine learning, such as bagging and boosting, aim to improve the generalization and robustness of models. They combine multiple models to reduce overfitting and improve predictive performance, making them a valuable tool for creating more accurate and reliable machine learning models.

Cassandra uses a columnar-based data model. This model allows for efficient data retrieval and storage, making it suitable for applications with high read and write workloads, such as time-series data or analytics.

The range of a dataset is calculated by subtracting the minimum value from the maximum value. This measures the spread of data from the smallest to the largest value, making option A the correct answer.

The main challenge addressed by the transformer architecture is capturing long-range dependencies in sequential data. Transformers use self-attention mechanisms to understand the relationship between distant words in a sentence, making them effective for various NLP tasks like machine translation and text summarization.

Relational databases are designed for storing structured data with well-defined rows and columns. This structured format allows for efficient storage and querying of data. Unstructured data, on the other hand, lacks a predefined structure.

To prevent SQL injection, you should sanitize and parameterize user inputs in your queries. This involves validating and escaping user input data to ensure that it cannot be used to execute malicious SQL commands. Other options, while important, do not directly prevent SQL injection.

NoSQL databases are schemaless, which means they do not require a fixed schema for data storage. This flexibility allows for the storage of various types of data without predefined structure constraints.